Gamma-Ray and High-Energy-Neutron Measurements on CORONAS-F during the Solar Flare of 28 October 2003

Abstract

The solar flare of 28 October 2003 (X17.2/4B) was recorded by the SONG instrument onboard the CORONAS-F satellite. A description of the SONG instrument, its in-orbit operation and the principal data reduction methods used to derive the flare gamma-ray properties are presented. Appreciable gamma-ray emission was observed in the 0.2 – 300 MeV energy range. Several time intervals were identified which showed major changes in the intensity and spectral shape of the flare gamma-ray emission. The primary bremsstrahlung proves to be extended to 90 MeV and dominates during 11:02:11 – 11:03:50 UT time interval, i.e. at the beginning of the flare impulsive phase. Afterwards, the SONG response was consistent with detection of the pion-decay gamma emission. A sharp increase in the pion-decay-generated gamma-ray emission was observed at 11:03:51±2 s UT, implying a substantial change in the spectrum of accelerated ions, which testified the appearance of protons with energies of >300 MeV on the Sun. This emission lasted at least 8 – 9 min until the end of our measurements. The ion acceleration to high energies was also proved by the detection of neutrons with energies >500 MeV. It was found that the most efficient acceleration of high-energy protons coincides in time with the highest rate of the magnetic-flux change rate. The maximum gamma-ray flux at 100 MeV was 1.1×10−2 photons cm−2 s−1 MeV−1, exceeding all the fluxes that have ever been recorded.